In hydraulic systems, for example, in the form of large gear units, the hydraulic media, such as lubricants or the like, are exposed to changing environmental conditions. The result can be an undesired introduction of particles, also in the form of water, into the lubricant. This state is basically associated with a degradation of the physical properties of the hydraulic media, in particular with respect to the targeted lubricating power of such lubricants. A typical representative problem constitutes the gear units of wind turbines. To transform the speed of a rotor of a wind turbine to a speed that is suitable for driving a generator, spur gear systems in the manner of planetary gear trains or systems comprising a pair of gear rings are customarily used. The rotor has a hub with two or more blades and has for the gear unit a drive with a high torque at a well-known very low speed. The gear unit in turn has for the generator a drive with a lower torque at, for example, a speed transformation of 80-fold.
For this reason, for more than 20 years, for example, planetary gear units, which are comparatively compact with respect to the installation requirement are used in practice. Such speed transforming gears are in many respects units with components that are exposed to stress, so that the wear of such units has to be minimized, because the maintenance, repair, and replacement of the key wear components of such gear units is often time consuming and cost intensive.
Since some of the components of such gear units stand as high as a man, they can be greased at the respective gearwheels and bearing locations either by oil recirculating lubrication systems with continuous transport and application of lubricant by gear oil pumps from a gear oil sump or by splash lubricating systems. In the case of splash lubricating systems, the gearwheels of the gear unit are partially immersed in immersion baths with a supply of lubricant.
Gear units, which are characterized in particular by a large volume or by large inner surfaces of the gear housing, tend to collect condensation water in their interior. This process is facilitated, especially in the case of iteratively operating gear units, by their episodically heating up and then subsequently cooling down.
Gear units of wind turbines are exposed, as a function of their installation site, more or less to cyclical operating and rest periods due to the fluctuation in the strength of the wind. In addition, even though these gear units are housed in system housings, for example, on a tower of a wind turbine, they are exposed more to the changing weather conditions, in particular the moist air, than is the case with other gear units, which are arranged stationarily in a defined environment. The result is that the water content in the lubricant of such gear units can increase. Water has an adverse effect on the physical properties of lubricants, such as gear oil, and can contribute to the premature aging of the lubricating oil, a feature that in turn has a damaging effect on the components of the gear unit.
In order to decrease the atmospheric moisture content in a gear housing and at the same time also the water content in the lubricating oil, for example, DE 100 31 004 B4 discloses use of a container with aluminum oxide that contains an absorptive agent for the humidity in the air. In the solution known from the prior art, the routing of the air flow is selected such that this air flows through the absorptive agent. Check valves are used for allowing the absorptive agent to flow through the container only when the air is delivered, but not when the air is removed. This arrangement prevents the oil laden air from flowing, for example, out of a gear sump, over which the dried air from the container sweeps.
In principle, EP 0 135006 A2 discloses configuring a device for aerating with dried air such that a chemically active desiccant is used, through which air flow can take place. As a result, the moisture is removed from this air. These prior art devices are suited for continuous operation with long maintenance intervals, the customary operating mode of a wind power system only under certain conditions. In addition, the volumetric flow rate of the dried air that is provided by such devices is limited.
EP 1 736 665 A2 discloses a method for removing the moisture inside the tower of a wind turbine. The prior art wind turbine comprises an interior, which is sealed off at least substantially against an air exchange, and a moisture extraction device. The moisture extraction device is connected to the interior by an inlet for moist air and an outlet for dry air, and is disposed between the moist air inlet and the dry air outlet. The moisture extraction unit known from the prior art draws off the moist air from the interior of the wind turbine, extracts water from the moist air, and returns the dried air back into the interior as a closed loop. A negative pressure area can be generated at the moist air inlet by sucking in the moist air from the interior. Correspondingly, an area exhibiting excess pressure can be generated at the dry air outlet by expelling the dried air into the interior. A drying air stream is then formed in the interior between the negative pressure area and the excess pressure area. The moisture extraction device extracts the moisture from the air from the interior and can comprise a heating unit.